Process for the photographic production of equidensities

ABSTRACT

The production of areas of equal density in a photographic image by combining in a photographic material two silver halide emulsions in one or two layers, one of which emulsions is more soluble in photographic developer than the other emulsion but the more soluble emulsion is lower in speed than the less soluble emulsion and the less soluble emulsion is present in a much smaller proportion. After the photographic material is exposed it is developed in a bath having a silver halide developing compound and a silver halide solvent for the slower halide emulsion so that the faster less soluble emulsion is developed in the exposed area to yield a negative silver image and the slower silver halide emulsion is physically developed to yield a positive image and chemically developed to yield a negative image. The developed material is finally fixed.

United States Patent [151 3,637,388

Ranz et a1. 1 Jan. 25, 1972 [54] PROCESS F THE H T H: 3,143,414 8/ 1964 Yacket et al... ..96/69 3,241,964 3/1966 Land ..96/61 PRODUCTION OF EQUIDENSITIES 2,251,965 8/1941 Verkinderen ..96/69 [72] Inventors: Erwin Ranz; Harald Von Rintelen;

Raymund Pfeiifenschneider, all of Lever- FOREIGN PATENTS OR APPLICATIONS kusen: Armin Voight, COIOgW-Stamm- 859,711 12/1952 Germany ..96/61 [73] Assignee: Agla-Gevaert Aktiengesellschaft, Lever- Primary Exami'ferwimam kusen, Germany Assistant Examiner-M. Sofocleous Attorney-Connolly and Hutz [22] Filed: Oct. 9, 1968 [2 l1 Appl. No.: 766,155 [571 B TRACT The production of areas of equal density in a photographic image by combining in a photographic material two silver ha- [30] Foreign Application Priority Data 1de emulslons In one or two layers, one of whlch emuls1ons 15 Dec. 18, 1967 Germany ..P 15 97 509.4 more soluble in photographic developer than the other emulsion but the more soluble emulsion is lower in speed than the [52] US. Cl ..96/66, 96/61, 96/69, less soluble emulsion and the less soluble emulsion is present 96/48 PD in a much smaller proportion. After the photographic material [51] Int. Cl ..G03c 5/30, G03c 1/02, G03c 5/38 is exposed it is developed in a bath having a silver halide [58] Field of Search ..96/61, 63, 69, 66, 48 PD developing compound and a silver halide solvent for the slower halide emulsion so that the faster less soluble emulsion [56] References Cited is developed in the exposed area to yield a negative silver image and the slower silver halide emulsion is physically UNITED STATES PATENTS developed to yield a positive image and chemically developed 3,140,179 7/1964 Russell ..96/69 Yield a negative image The devekPed material is finally 2,805,947 9/1957 Mease fixed- 3,505,068 4/1970 Beckett et al ..96/69 6 Claims, 1 Drawing Figure U1 2 ll-l Q LOG IXT PROCESS FOR THE PHOTOGRAPIIIC PRODUCTION OF EQUIDENSITIES The invention relates to a process for the production of photographic equidensity images and to a photographic material for performing said process.

It is already known that lines of equal density (equidensities) can be obtained from an original by photographic processes. An equidensometric process may be used in many ways, e.g., for increasing the accuracy of measurements in interpreting interferographs, in sensitometry, in photometry, in

astronomy, in carrying out the photometry of spectral lines, in high accuracy measuring techniques, (profile examinations, surface examinations), in the examination of optical systems, and in the production of aerial photographs.

In the simplest photographic process for producing equidensities firstly a transparent positive is produced from a negative, and the two are then placed on top of each other, either exactly in alignment or slightly out of alignment. A copy of this negative-positive combination will then serve as a type of equidensity. Unfortunately, it is difficult to accurately align the negative and the positive and to obtain the optimum spacing between the two layers. This may lead to inaccuracies in the copy.

very little margin in the processing. Furthermore, emulsions provide a sufficient Sabattier effect.

Methods for the photographic production of equidensities are fully described in Die Aquidensitometrie by E. Lau and G. Krug (publishers Akademie-Verlag Berlin, 1957).

The production of direct positives by the so-called bromine ion diffusion process is described in German Pat. No. 859,71 1. In this process, direct positive images are obtained when a layer which comprises a silver chloride emulsion (about 95 percent of very low sensitivity, a preferably optically sensitized silver bromide emulsion (approximately 5 percent) of high sensitivity and nuclei for physical development, e.g., colloidal silver, is exposed and developed using a developing agent which does not contain bromide but which contains a large amount of sulfite. The exposure is adjusted according to the sensitivity of the silver bromide emulsion. No bromine ions are formed in the areas which are not exposed or which are insufficiently exposed. The silver chloride emulsion, in this case, is physically developed on the nuclei. If the exposure lies within the sensitivity range of the sensitized silver bromide emulsion, free bromine ions are formed in the layer on development, and the physical development of the silver chloride on the nuclei is prevented. A direct positive image of very steep gradation and a grey fog which is caused by development of the silver bromide emulsion which is present in small quantities, are thereby obtained.

It is among the objects of the invention to provide new processes for the production of equidensity images which can be carried out in a simple mannerby the usual photographic processing methods.

We now have found that equidensity images can be obtained in a simple manner by photographic methods by exposing a photographic material in the form of one or two silver halide emulsion layers, the one of which contains a silver halide emulsion which is more soluble in the developer bath than another silver halide component, the concentration of which is up to percent by weight based on the total weight of the emulsion, whereby the more soluble silver halide emulsion has very few a speed which is lower preferably by the factor l:l-20 than the speed of the less soluble emulsion.

According to a preferred embodiment the silver halide emulsion layer contains up to 99 percent by weight of a relatively high-sensitive silver chloride emulsion and a lower proi by weight, of a relatively insensitive silver bromide emulsion, and which is processed with a developer solution which does not contain any potassium bromide. The sensitivity of the silver chloride emulsion should only be slightly less than that of the silver bromide emulsion. Sensitivity ratios of the silver chloride emulsion to the silver bromide emulsion towards white light of 1:10 to 9zl0 have been found to be particularly suitable.

As to suitable silver halide emulsions or mixtures of silver halide emulsions, we refer to German Pat. No. 859,71 1, particularly page 2, lines 22 seq.

According to a preferred embodiment, the emulsions which are to be used in the process according to the invention contain development nuclei of the usual type, e.g., those which are used in positive materials for the silver salt diffusion process, such as finely divided metals, especially silver, or their sulfides and/or selenides. In principle, one could also use silver chloride emulsions which do not contain nuclei since a pure silver chloride emulsion can already be developed physically in the absence of bromine ions, but the densities then obtained are insufficient for many purposes.

Further suitable emulsions include combinations of silverchloride bromide with silver bromide iodide or silver bromide with silver bromide iodide. It is essential only the more sensitive silver halide emulsion to be less soluble in the developer bath than less sensitive emulsion.

The two emulsions may be present as a mixture in the same layer, or they may be present in separate layers, in which case the less soluble emulsion e.g., silver bromide emulsion preferably forms the outer layer and the more soluble, e.g., silver chloride emulsion, containing nuclei if necessary, forms the under layer.

The mode of operation of the photographic materials which are to be used according to the invention can be seen from the attached FIGURE. This FIGURE shows the characteristic curve in which the log lXt value is plotted as the axis of abscisdevelopment. The low density of the silver bromide emulsions is the only density which is therefore obtained in the exposed areas. At higher intensities of exposure, chemical development of the silver chloride emulsion sets in which leads to an image represented by curve 3 in the diagram. The figure also shows the characteristic curves of a photographic material used for the production of equidensities, when images of surfaces or lines of equal densities of the original are formed. In this case, thus only light of a certain intensity range is recorded and the silver halide emulsion layer is blackened by light of lower (physical development-curve l) and higher energy (chemical developmentcurve 3).

According to a preferred embodiment of the invention, the silver chloride emulsions are additionally spectrally sensitized in the green and/or red region of the visible spectrum. Thus the emulsion is ortho and/or panchromatically sensitized. The silver chloride emulsion should be more sensitive to light of wavelengths higher than about 500 m./p. than the silver bromide emulsion.

With such a material, the range of log IXt values to be recorded can be varied as required by using filters. If, for example, exposure is carried out through a yellow filter which is transparent to light of wavelengths of over 500 mm, the relative sensitivity of the blue sensitive silver bromide emulsion is lowered. This effect is illustrated in the FIGURE When exposure behind a yellow filter is carried out, the characteristic curve of silver bromide emulsion 2 is shifted into the region of higher light energy. Curve 4, for example, is obtained. This also causes the positive characteristic curve I to be shifted to the right. With such exposure, the positive characteristic curve 5, for example, is obtained. The FIGURE shows that the recorded range of log IXt values is very narrow, as is indicated by the gap between the curves 3 and 5.

The equidensities thus become increasingly narrower with increasing density of the yellow filter so that, for example, a range of exposure of only 1:1.2 only (one step of a DIN wedge) or less is recorded as equidensity. The required breadth of equidensity can thus be adjusted by suitable choice of absorption characteristic of the filter. A similar procedure can be employed for panchromatic sensitization, e.g., using a red filter.

The characteristic difference between the process according to the invention and the known bromine ion diffusion process is that in the conventional process for the production of direct positive images, the silver chloride emulsion is only developed physically, i.e., only a positive characteristic'curve is obtained. In the present invention, on the other hand, the silver chloride emulsion serves a further purpose, i.e., it is also developed chemically and therefore a negative characteristic curve is obtained in addition. The reason for this effect is that the silver chloride emulsions used for the process according to the invention have a much higher sensitivity than those used in the conventional bromine ion diffusion processes.

The emulsions to be used in the process according to the invention are prepared in the usual manner. The usual hydrophilic binding agents may be used, especially gelatin. The emulsions may contain the usual additives such as chemical sensitizers, stabilizers, hardeners etc. The light sensitive layers may also be applied to the usual supports, e.g. supports of cellulose ester, polyester. Supports made of polyethylene terephthalate, glass or paper are particularly preferred.

The usual sensitizers may be used for spectral sensitization of the silver chloride emulsions. It has also been found advantageous to sensitize the silver bromide emulsion used in its own range of sensitivity, i.e., in the blue region of the spec trum, by the addition of sensitizers because this improves, in particular, the stability of the characteristic curve and the sensitivity of the silver bromide emulsion when stored for prolonged periods.

The y-values of the positive and negative characteristic curves depend primarily on the 'y-values of the emulsion for example the silver chloride and silver bromide emulsion used. it is therefore possible to influence them in the desired direction in the usual manner by suitable choice of the emulsions.

It is, of course, also possible to produce colored equidensity images if the material is processed by color-forming photographic processes in the usual manner. in such a case, the color coupler may be added to the emulsion or to the developer solution and processed in known manner with developers which lead to formation of colored images. The use of the material according to the invention enables areas of equal wavelengths of light.

If the filter density is not changed but, for example, higher exposure times are employed, the equidensity appears in the higher densities of the original, the breadth of the equidensity remaining constant. By superimposing the copying of different exposed equidensity layers which have been cast on film supports, groups of curves are obtained which accurately correspond to the peaks and troughs of the object under study.

If an equidensity which has been obtained on a developed equidensity film is copied in accordance with the present invention on to yet another equidensity layer, equidensities of the second order are obtained, and when these in turn are copied one obtains equidensities of the third order etc., which then become extremely sharp.

Compared with the known processes for obtaining equidensities, the process according to the invention has the great advantage of producing equidensities in a layer immediately after imagewise exposure and it is therefor particularly simple. The position of the equidensities depends only on the exposure, and, in the sensitized emulsions, the breadth of the equidensities depends only on the filter density employed. The uncertainty factors which necessitate a diffuse second exposure (Sabattier effect) are eliminated. Very narrow equidensities with steep gradations can be produced.

The developer solutions used have the usual compositions employed for the bromine ion diffusion process. The following compounds, for example, may be used as developing agents: Hydroquinone, developers of the aminophenol series, e.g., pmethylaminophenol, p-phenyldiamine derivatives, developers of the pyrazolidone series, e.g., l-phenylpyrazolidone-3 and others, alone or in mixtures with each other.

The potassium bromide content should not exceed 50 mg. per liter.

The developer must be capable of dissolving the more soluble silver halide but essentially not the less soluble silver halide.

The silver halide solvent which has to be present in the developer composition depends on the silver halide of the emulsions.

A suitable solvent for silver chloride silver bromide is, for example, sodium sulfite in concentrations of about l to g./liter of developer solution. in the case of silver bromide/silver iodide emulsions a sodium thiosulfate containing developer is suitable.

If the developing agent or other additives can themselves act as silver halide solvents, as in the case of p-phenylenediamine or its derivatives, the addition of silver halide solvents may be omitted.

The developer solutions also contain the usual quantities of sequestering agents, antioxidants and substances which render the medium alkaline, etc. The pH of the developer solution is between about 8.5 and l2.5.

EXAMPLE I A silver chloride gelatin emulsion is mixed with gelatin silver bromide gelatin emulsion in a ratio of 201l. The sensitivity of the silver bromide emulsion is in the region of 1 DIN above that of the silver chloride emulsion. Both the emulsions are prepared in the usual manner. 0.06 g. of colloidal silver selenide which has been precipitated in gelatin solution are added to 1 liter of this mixture as development nuclei. The emulsion is applied onto a barytacoated paper support, the amount of silver applied being about 2 g. of silver per m The film is exposed to light and developed with the following developer solution at 20C.

water i l.

hydroquinone 9 g. ethylenediamiotetracetic acid i g. l-phenyl-pyrawlidone-3 0.5 g. anhydrous sodium sull'lte l20 g. soda 60 g. sodium hydroxide 2 3.

Development is then stopped in 2 percent acetic acid is fixed, washed and dried.

Sharp equidensities of excellent quality are obtained.

EXAMPLE 2 The same procedure is employed as in example 1 except that no nuclei are added to the emulsion. The equidensities obtained after exposure and development, have a density of the physically developed silver considerably lower than in example 1.

EXAMPLE 3 A high-contrast silver chloride emulsion which has been sensitized with a sensitizer of the following formula for the green region of the spectrum culls-S N falia is mixed with a nonsensitized silver bromide emulsion in a ratio of 20:1. Both emulsions are prepared by known processes. 0.12 g. of colloidal silver selenide are added to 1 liter of this mixture in the manner described in example 1.

The sensitivity of the sensitized silver chloride emulsion is 1/10 of the sensitivity of the silver bromide emulsion. The emulsion mixture is applied onto a support of polyethylene terephthalate in a quantity of about 4 g. of silver per m After exposure to white light and development as indicated in example 1, very broad equidensities with a steep characteristic curve are obtained. If exposure is carried out behind a yellow filter, the equidensities become increasingly narrower with increasing absorption of the filter density. Equidensities which have a width variable from a maximum exposure range of 1:10 to a very narrow exposure range of above 1:1.2 can be obtained in this example by suitable choice of the yellow filter density.

EXAMPLE 4 The same procedure is employed as in example 3 except that the silver chloride emulsion is also sensitized to light from the red region of the spectrum. After exposure behind a red filter and development as in example I, the width of the equidensities can be adjusted to the required values as described in example 3.

EXAMPLE 5 A green-sensitive gelatin silver chloride emulsion which has been prepared in the usual manner is applied onto a transparent support of cellulose acetate after 0.1 g. of colloidal silver has been added per liter of emulsion. This layer is coated with a thin layer of a non-sensitized gelatin silver bromide emulsion the sensitivity of which to white light is about times the sensitivity of the silver chloride emulsion. After exposure and development as in example 1, equidensities are obtained the breadth of which can be varied with the density of the yellow filter employed, as described in example 3.

EXAMPLE 6 A gelatino silver chloride emulsion is mixed in the ratio of 1021 with a gelatino silver chlorobromide emulsion the sensitivity of which is about 0.5 DIN higher than that of the silver chloride emulsion. 0.2 g. of colloidal gold are added to 1 liter of this mixture. It is cast on a baryta-coated paper support.

The layer is exposed and developed at C. in a developer solution of the following composition:

Water I l.

p-melhylaminophenol 3 g. soda 20 g. anhydrous sodium sulfih: g. sodium chloride 0.5

Development is stopped in 2 percent aqueous acetic acid and the layer is then fixed. Narrow equidensities are obtained.

EXAMPLE 7 A gelatino silver chloride emulsion is mixed with a gelatino silver bromide emulsion in the ratio of 20: 1. Both emulsions are sensitized to light from the green region of the spectrum by the addition of a sensitizer of the following formula:

so that on exposure to green light, the silver bromide emulsion is about 1%" DIN more sensitive than the silver chloride emulsion. 0.1 g. of colloidal gold and 20 g. ofa magenta coupler of the following formula are added to 1 liter of this mixture:

SOaH 7 It is cast on a transparent support of polyethylene terephthalate, 3 g. of silver being applied per m A yellow filter layer which contains a yellow dye of the following formula Water 1 l. N,N-diethyl-p-phenylenediamine 3 g. p-Methylaminophenol 0.05 g anhydrous sodium sulfile 3 g. soda 4 g.

Development is stopped in 2 percent aqueous acetic acid solution. Further processing is performed according to conventional color negative processing.

EXAMPLE 8 The same procedure is employed as in example 1 except that the silver bromide emulsion is sensitized to the blue region of the spectrum in the region of its own sensitivity with a sensitizer of the following formula:

The sensitometric properties (characteristic curve) and the sensitivity of the silver bromide emulsion obtained is more stable.

We claim: I. Process for the production of equidensity images including the steps of exposing to the original from which an equidensity image is to be made a photographic material containing two silver halide emulsions mixed in one layer or in two layers, whereby l. 90 to 99 percent by weight based on the total weight of the emulsions consist of a light sensitive, slower silver halide emulsion which is more soluble in the developer bath, and

2. up to 10 percent by weight based on the total weight of the emulsions consist of a light sensitive, faster silver halide emulsion containing a different silver halide which is less soluble in the developer bath, said more soluble light sensitive, slower silver halide emulsion having a sensitivity to white light lower by the factor of at least 1.1 than the sensitivity of the less soluble light sensitive, faster silver halide emulsion, developing the exposed material in a aqueous developer bath including a silver halide developing compound and a silver halide solvent for the slower silver halide emulsion, whereby the slower silver halide emulsion is physically developed to yield a positive silver image and additionally chemically developed to yield a negative silver image and whereby the faster silver halide emulsion is developed in the exposed areas to yield only a negative silver image and finally fixing the developed material.

2. The process of claim 1, wherein the more sensitive emulsion is a silver chloride emulsion, the less sensitive emulsion is a silver bromide emulsion, and the aqueous developer bath is substantially free of bromide ions.

3. The process of claim 1, wherein the more soluble silver halide emulsion has a sensitivity to white light which is lower by the factor l:l-20 than the sensitivity of the less soluble emulsion.

4. Process of claim 2, wherein the sensitivity ratios of the silver chloride emulsion to the silver bromide emulsion towards white light are l:l0 to 9:10.

5. Process of claim 1, wherein the more soluble silver halide emulsion contain development nuclei.

6. Process of claim 2, wherein the silver bromide emulsion is spectrally sensitized to light from the blue region of the spectrum and the silver chloride emulsion is, in addition, spectrally sensitized to light from the green and/or red region of the visible spectrum. 

2. up to 10 percent by weight based on the total weight of the emulsions consist of a light sensitive, faster silver halide emulsion containing a different silver halide which is less soluble in the developer bath, said more soluble light sensitive, slower silver halide emulsion having a sensitIvity to white light lower by the factor of at least 1.1 than the sensitivity of the less soluble light sensitive, faster silver halide emulsion, developing the exposed material in a aqueous developer bath including a silver halide developing compound and a silver halide solvent for the slower silver halide emulsion, whereby the slower silver halide emulsion is physically developed to yield a positive silver image and additionally chemically developed to yield a negative silver image and whereby the faster silver halide emulsion is developed in the exposed areas to yield only a negative silver image and finally fixing the developed material.
 2. The process of claim 1, wherein the more sensitive emulsion is a silver chloride emulsion, the less sensitive emulsion is a silver bromide emulsion, and the aqueous developer bath is substantially free of bromide ions.
 3. The process of claim 1, wherein the more soluble silver halide emulsion has a sensitivity to white light which is lower by the factor 1:1-20 than the sensitivity of the less soluble emulsion.
 4. Process of claim 2, wherein the sensitivity ratios of the silver chloride emulsion to the silver bromide emulsion towards white light are 1:10 to 9:10.
 5. Process of claim 1, wherein the more soluble silver halide emulsion contain development nuclei.
 6. Process of claim 2, wherein the silver bromide emulsion is spectrally sensitized to light from the blue region of the spectrum and the silver chloride emulsion is, in addition, spectrally sensitized to light from the green and/or red region of the visible spectrum. 